1. Field of the Invention
This invention relates to a bearing seal for a rotatable member assembly and more particularly to a seal for the main bearing of a drill head assembly in which the seal is positioned between a rotatable cover plate and a stationary bearing carrier and is operable to convert lateral and vertical thrust forces applied to the cover plate by a drill steel to external free rolling forces which substantially reduce wear and deterioration of the bearing seal in underground mine drilling operations.
2. Description of the Prior Arts
In rock drilling operations, as encountered in underground mining and excavating, it is the conventional practice to drill holes in a rock formation by a rotary drill assembly or by a rotary percussion drill assembly. U.S. Pat. Nos. 3,547,206 and 3,654,961 are examples of such drill assemblies which include a drill pot that carries a hydraulic motor having a motor shaft nonrotatably connected to a bevel gear which meshes with another bevel gear rotatably journaled on a support member or hub within the drill pot housing. The hub is fixed to a rotatable head or pot cover and has a seat into which the shank of a drill steel is received. A drill bit is positioned on the upper end of the drill steel. With this arrangement rotation of the motor shaft is transmitted to the drill steel to rotate the drill bit.
Generally the drill assembly is incorporated with a self-propelled machine that maneuvers the drill pot into position and moves the drill pot in the axial direction of advancement of the drill bit into the rock formation. For rock drilling operations in an underground mine the drill assembly is supported by a boom that is pivotally mounted on the front of a mobile frame. Upward pivotal movement of the boom moves a drill steel seated in the pot cover into drilling position. As the drill steel rotates, the boom exerts upward pressure upon the drill assembly to increase the driving thrust upon the drill steel. This advances the drill steel vertically into the rock formation as rock material is dislodged to form an elongated bore in the rock formation. The upward force exerted upon the drill assembly by the boom overcomes the resistance encountered by the rock structure to rotation of the drill bit. An example of such a drilling machine is disclosed in U.S. Pat. No. 3,190,369.
As the drill bit advances into the rock formation by the upward thrust applied by the drill boom, the resistive forces encountered exert tremendous lateral and vertical thrust forces on the drill steel. These thrust forces are transmitted through the drill steel to the drill retaining member and to the main bearings which rotatably support the drill retaining member. The effect of the lateral and vertical thrust forces is to apply a dry rubbing motion upon the drill retaining member and the conventional lip seal that is positioned between the rotatable cover plate and the stationary bearing carrier to seal the upper main bearing. The lateral and vertical thrust forces promote wear of the conventional lip seal particularly in view of the dry and dusty atmosphere encountered in mine drilling operations where wear of the lip seal is accelerated.
The failure of the lip seal results in deterioration of the seal for the main bearing thus exposing the main bearing to dust contamination and eventual failure with resultant damage to the drive gearing. Also failure of the lip seal and damage to the main bearing is known to result in misalignment of the drill retaining member from an axial position in the drill housing. This causes grooving of the drill retaining member and the shank of the drill steel.
Failure of the lip seal requires that the drill head assembly be removed from operation for replacement of the lip seal. This must be done frequently to prevent damage to the main bearings. However, in the event that the main bearings become damaged, the main bearings must be replaced. Also the entire drill head assembly must be disassembled to remove the contaminants that have entered the drill housing chamber. These repair operations are costly and time consuming.
While it has been suggested by the known devices to provide seal assemblies for bearings used in rotatable drill heads, the known devices require substantial modification to the bearing carrier in order to accommodate the seal assembly. Known arrangements for sealing a bearing that supports a rotatably driven shaft such as the shank of a drill steel in a drill head assembly are disclosed in U.S. Pat. Nos. 2,667,388; 2,712,970; 2,913,289; 3,218,110; 3,861,765; 4,060,289; 4,084,861; and 4,092,054. Each of these devices utilize various seal arrangements as an additional element separate and distinct from the bearing.
Therefore, there is need to provide for a rotatable drill head assembly, a bearing seal adaptable to replace the conventional lip seal without requiring modifications to be made to the internal structure of the drill head assembly and perform the dual purpose of a seal for the main bearing and a sealing member to transmit the lateral and vertical thrust forces generated by the drill steel to the main bearing without damage to the bearing seal.